1. Field of the Invention
The present invention relates to a gas concentration measuring apparatus.
2. Description of the Related Art
Apparatuses exist that are configured to measure concentrations of various gasses. For example, when refined air (medical air) is prepared onsite at a medical facility, the medical air can be prepared using an apparatus that mixes 100% O2 gas from a gas cylinder with 100% N2 gas from a gas cylinder at a prescribed ratio. Alternatively, the medical air can be prepared using an air refining apparatus that is capable of performing compressing, drying, and dust processing functions. In either of these apparatuses, the concentration of carbon dioxide (CO2) in the prepared medical air is measured continuously and controlled so that the amount of CO2 does not exceed a prescribed maximum of, for example, 500 ml/m3 (500 ppm).
A CO2 analyzer can also be provided in an apparatus, such as a photosynthesis evaluation apparatus, for evaluating a CO2 absorption or CO2 emission function of a plant. The evaluation apparatus can be, for example, an apparatus such as that disclosed in Laid-open Japanese Patent Application 2010-10. That is, the evaluation apparatus can be configured to evaluate a CO2 absorption function or a CO2 emission function of a plant during photosynthesis in a natural environment. A CO2 analyzer can be provided among the components of the evaluation apparatus for measuring a CO2 concentration to determine the CO2 absorption function or the CO2 emission function of the plant with a high degree of measurement accuracy.
In such an apparatus, a sample gas can be measured by measuring a CO2 concentration using a non-dispersive infrared absorption technique that can be performed by an apparatus as shown, for example, in FIGS. 10 and 11. That is, the gas concentration measuring apparatus 13 includes a light source unit 15 in which a light source 14 is arranged, a light shuttering device 16 that is configured to block or pass light as necessary, a sample cell unit 17 in which a sample cell is arranged, and a concentration measuring sensor 18 (detection device).
In order to measure CO2 and other components contained in atmospheric air in minute amounts, a highly sensitive measurement is typically necessary because the contents of such components are on the order of only several hundred parts per million. Therefore, a Kanthal wire or other filament that emits a large amount of light is used as the light source 14, and a chopper or other light shuttering device 16 is provided to block the light intermittently as necessary. If a chopper is used, a motor and an external electric power source are provided to drive the chopper. Thus, the number of parts of the gas concentration measuring apparatus 13 will be increased. As a result, it will be easier for a gap S to form between the sample cell and the concentration measuring sensor 18.
Also, while the concentration of CO2 in atmospheric air is generally approximately 300 to 400 ppm, the concentration of CO2 in a person's breath is several percent. Consequently, if the gas concentration measuring apparatus 13 is installed in a place where people come and go and/or the gas concentration measuring apparatus 13 is operated by a person, then the concentration of CO2 surrounding the gas concentration measuring apparatus 13 will typically fluctuate. Similarly, if a combustion apparatus is installed near the gas concentration measuring apparatus 13, then the concentration of CO2 surrounding the gas concentration measuring apparatus 13 will rise and the concentration of CO2 surrounding the optical system (in particular, the concentration measuring sensor 18) will fluctuate, thus making it difficult to measure the CO2 concentration accurately.
Additionally, even if the apparatus is installed in a location where access by people is restricted, a standard concentration of CO2 for the inside of designated buildings (e.g., commercial facilities and offices) is stipulated to be 1000 ppm or less according to typical building management laws. However, this concentration is higher than the standard for medical air. Consequently, even if the gas concentration measuring apparatus 13 is installed in a place where access restricted, there is a possibility that the concentration of a targeted measurement substance cannot be measured with sufficient stability or accuracy. In an attempt to avoid these issues, the entire gas concentration measuring apparatus 13 can be enclosed in an apparatus housing case 19 as shown in FIG. 10. The apparatus housing case 19 is completely sealed to prevent ambient air from flowing into the gas concentration measuring apparatus 13. For example, all gaps are filled with a sealing material, and each gap of the analyzer is purged with N2 or another inert gas, such as that described in Japanese Examined Patent Publication No. S64-002889.
Furthermore, the problems discussed above are not limited to measuring the concentration of CO2 in medical air, but also occur when measuring the concentration of H2O in air. The same or similar problems also exist when measuring a CO2 concentration in order to understand a CO2 absorption or emission function of a plant using the aforementioned photosynthesis evaluating apparatus.